I'm getting this error when trying to use this function with PHP 5:

Fatal error: Call to undefined function imagecreatefromjpeg()
EDIT: I now know that I need to enable GD, what I don't know, is why this isn't enabled already in PHP 5, I can't find anything but the GD2 dll in the ini.

Here is the configure command out of phpinfo:
cscript /nologo configure.js "--enable-snapshot-build" "--with-gd=shared"